How to disassemble, clean, rebuild, and reassemble trim motors

[BlueFishCrisis]

My trim motor was blowing fuses, so I had to remove and inspect. It was from a 95 SL750 originally, so I assume the arrangement of a Fast Trim Version is different.

Figured I would document it along the way.

This thread will outline how to disassemble, clean, rebuild, and reassemble trim motors after removal from the ski, with replacement parts for the DC electric motor and oil seal.

Start by removing the 5 screws securing the black plastic housing cover to the mount plate.



Next remove the motor leads and ensure the gasket is present and intact.



Next you need to remove the spring clutch on the actuator arm. I used a C clamp to relieve the pressure to make it easy to remove the pin.

[BlueFishCrisis]

Remove the actuator arm and spring.



Next remove the 4 screws holding the gearbox to the mount plate. Note that these 4 screws along with the output shaft present an opportunity for the trim motor to leak as they are submerged when floating or at idle. The screws I removed appeared to contain a small fiber washer along with loctite.



Separate the mounting plate from the gearbox housing. Note the oil seal in the mounting plate.



If the oil seal is cracked or worn, remove by driving out with a 12 mm socket.

[BlueFishCrisis]

Removed oil seal.



Seal is 3/4" OD x 1/4" thick. Output shaft is 3/8" Seal appears to have a double lip and spring retainer. McMaster Carr 5154T31 is the correct replacement.

Remove the four 1/4" hex head screws holding the case halves together, then separate the case halves and ensure to push down on the output shaft to try and keep it in the "bottom" of the case.

[BlueFishCrisis]

Case opened, with all gears residing on the "bottom" half. This is the half that the motor attaches to. This trim motor was in good operational condition.



This one was not....



For the next few steps, I have already fully disassembled, cleaned, and reassembled the gearbox so you can clearly see each component as we go through disassembly. Keep in mind that small parts like washers and spacers can get buried in the grease and corrosion. I will identify each of the small parts as we go so you can be sure to capture them during disassembly.

Clean gearbox ready for disassembly.

[BlueFishCrisis]

Note the thin washer on the output shaft. This can sometimes stick to the top of the housing. Be sure to locate it before moving forward. Remove the washer if it is on the output shaft.



Next remove the gear in the upper left corner.



Note the spacer under this gear. This one was stuck in place, so I did not remove it.



First gear removed.

[BlueFishCrisis]

Next remove this large spacer.



This is the next to go

[BlueFishCrisis]

Watch out for this spacer. It may be buried in grease.



Remove the gear that spacer was sitting on next.



Note the very thin washer underneath. It is easy to lose this in the cleanup process as well.

[BlueFishCrisis]

Last one to go before the output shaft. Note the small diameter gear and how long it is. This will help identify during reinstall.



Finally remove the output shaft. Note the thin washer on the bottom of the output shaft.

[BlueFishCrisis]

Also note the collar on the output shaft.




With all parts removed, you can see the two screws securing the motor. If the motor is seized, remove these two screws.



Mabuchi RS-555SH is no longer available. I have ordered a Mabuchi RS-555PH as a replacement.

This completes disassembly.

[waterdog1971]

I've meant to ask about this before, does the trim motor only work with the mfd or is it supposed to work all the time?

[BlueFishCrisis]

This trim motor will only operate when the engine is running, but does not require an MFD to be connected. The MFD simply senses the "on" voltage and moves the meter at a specified rate while the up or down trim buttons are held. Only the oval MFDs have the trim position display, but there are mechanical indicators used with the round MFD or analog gauges.

[waterdog1971]

ok, thanks, there's a taped spot in the wire, i'll look at that and then follow this procedure you've laid out, thanks again

[Mr. GP1800]

I have actually connected the orange power feed for the trim switch to the red/purple to allow the trim to be operated whenever you wanted it to. The only problem there is if you operate the trim while the MFD is asleep, you will lose the sync with the MFD.

[waterdog1971]

I have actually connected the orange power feed for the trim switch to the red/purple to allow the trim to be operated whenever you wanted it to. The only problem there is if you operate the trim while the MFD is asleep, you will lose the sync with the MFD.

That's a thought since my mfd is fried and I won't have one till I save up to get a virage version from John and do the conversion. Thanks for the tip.

[waterdog1971]

Took my trim motor apart, gray goo everywhere and the gears were corroded as well as the motor and it was locked up but to my surprise I put it in the vise and tried to move a little at a time and it broke free, I put 12 volts to it and it spun like a top. I cleaned all the gears, lightly greased them and put it back together, then I put 12 volts to again fully assembled and it works great, thanks blue for laying out the procedure, good info.